Fully handle inner/outer determination and nesting in contour tracing

examples/contours.rs

@@ -15,22 +15,29 @@ const INNER: image::SRGBA = image::SRGBA {
     a: 1.0,
 };
 
+fn draw(contour: &contour::Contour, img: &mut image::Image<image::SRGBA>) {
+    let n = contour.vertices.len();
+    for i in 0..n {
+        let (x0, y0) = contour.vertices[i];
+        let (x1, y1) = contour.vertices[(i + 1) % n];
+        let colour = match contour.kind {
+            contour::Kind::Outer => OUTER,
+            contour::Kind::Inner => INNER,
+        };
+        draw::line(x0, y0, x1, y1, img, colour);
+    }
+}
+
 fn main() -> std::process::ExitCode {
     common::process_image(|mut img| {
         let greyscale = img.map(|p| image::Luminance::from(p));
-		let thresholded = filter::threshold_auto(greyscale);
+        let thresholded = filter::threshold_auto(greyscale);
+
         let contours = contour::find(thresholded);
         for contour in contours {
-			let n = contour.vertices.len();
-			for i in 0..n {
-				let (x0, y0) = contour.vertices[i];
-				let (x1, y1) = contour.vertices[(i + 1) % n];
-				draw::line(x0, y0, x1, y1, &mut img, match contour.kind {
-					contour::Kind::Outer => OUTER,
-					contour::Kind::Inner => INNER,
-				});
-			}
+            draw(&contour, &mut img);
         }
+
         img
     })
 }

src/contour.rs

@@ -18,7 +18,8 @@ pub struct Contour {
 enum Pixel {
     Foreground,
     Background,
-    Traced(usize),
+    TracedUp(usize),
+    TracedDown(usize),
 }
 
 #[derive(Clone, Copy, Debug, PartialEq)]
@@ -60,14 +61,14 @@ pub fn find(img: image::Image<image::Luminance>) -> Vec<Contour> {
             let q = (x, y);
             if foreground(&map, q) && background(&map, q.prev_x()) {
                 add(q, Kind::Outer, parent, &mut contours, &mut map);
-            } else if foreground(&map, q) && background(&map, q.next_x()) {
+            } else if (foreground(&map, q) || traced_up(&map, q).is_some())
+                && background(&map, q.next_x())
+            {
                 add(q, Kind::Inner, parent, &mut contours, &mut map);
-            } else if let Some(label) = traced(&map, q) {
-                if background(&map, q.prev_x()) {
-                    parent = Some(label);
-                } else if background(&map, q.next_x()) {
-                    parent = contours[label].parent;
-                }
+            } else if let Some(label) = traced_up(&map, q) {
+                parent = Some(label);
+			} else if let Some(label) = traced_down(&map, q) {
+                parent = contours[label].parent;
             }
         }
     }
@@ -103,7 +104,9 @@ fn trace(
 
     let mut vertices = Vec::new();
     loop {
-        q.set(img, Pixel::Traced(label));
+		if foreground(img, q) {
+			q.set(img, Pixel::TracedUp(label));
+		}
 
         let prev_dir = dir;
         dir = dir.flip().next();
@@ -115,6 +118,9 @@ fn trace(
                 }
                 break qp;
             }
+            if dir == Dir::E {
+                q.set(img, Pixel::TracedDown(label));
+            }
             dir = dir.next();
         };
 
@@ -122,9 +128,27 @@ fn trace(
             if dir != start_dir {
                 vertices.push(q);
             }
-            break vertices;
+            break;
         }
     }
+
+    // println!();
+    // for y in 0..img.extent.y {
+    //     for x in 0..img.extent.x {
+    //         if let Some(label) = traced_up(img, (x, y)) {
+    //             print!("{:1}", label);
+    //         } else if let Some(label) = traced_down(img, (x, y)) {
+    //             print!("-")
+    //         } else if foreground(img, (x, y)) {
+    //             print!(".");
+    //         } else if background(img, (x, y)) {
+    //             print!(" ");
+    //         }
+    //     }
+    //     println!();
+    // }
+
+	vertices
 }
 
 fn foreground(img: &image::Image<Pixel>, q: (usize, usize)) -> bool {
@@ -141,9 +165,19 @@ fn background(img: &image::Image<Pixel>, q: (usize, usize)) -> bool {
     }
 }
 
-fn traced(img: &image::Image<Pixel>, q: (usize, usize)) -> Option<usize> {
+fn traced_up(img: &image::Image<Pixel>, q: (usize, usize)) -> Option<usize> {
     match q.get(img) {
-        Some(Pixel::Traced(label)) => Some(label),
+        Some(Pixel::TracedUp(label)) => Some(label),
+        _ => None,
+    }
+}
+
+fn traced_down(
+    img: &image::Image<Pixel>,
+    q: (usize, usize),
+) -> Option<usize> {
+    match q.get(img) {
+        Some(Pixel::TracedDown(label)) => Some(label),
         _ => None,
     }
 }